download 속도제한

<?
$download_size = 312; //다운로드 속도제한 (KB)
$file = "./$download_file"; //서버내 존재하는 파일명
$dnfile =  "file_name"; //업로드당시 파일명 - 다운로드시 출력될 파일명

if(!is_file($file)) win_close("파일이 존재하지 않습니다.");

if(eregi("(MSIE 5.0|MSIE 5.1|MSIE 5.5|MSIE 6.0)", $HTTP_USER_AGENT)){
 if(strstr($HTTP_USER_AGENT, "MSIE 5.5")) {
  header("Content-Type: doesn/matter");
  header("Content-disposition: filename=$dnfile");
  header("Content-Transfer-Encoding: binary");
  header("Pragma: no-cache");
  header("Expires: 0");
 }

 if(strstr($HTTP_USER_AGENT, "MSIE 5.0")) {
  Header("Content-type: file/unknown");
  header("Content-Disposition: attachment; filename=$dnfile");
  Header("Content-Description: PHP3 Generated Data");
  header("Pragma: no-cache");
  header("Expires: 0");
 }

 if(strstr($HTTP_USER_AGENT, "MSIE 5.1")) {
  Header("Content-type: file/unknown");
  header("Content-Disposition: attachment; filename=$dnfile");
  Header("Content-Description: PHP3 Generated Data");
  header("Pragma: no-cache");
  header("Expires: 0");
 }

 if(strstr($HTTP_USER_AGENT, "MSIE 6.0")) {
  Header("Content-type: application/x-msdownload");
  Header("Content-Length: ".(string)(filesize("$file")));
  Header("Content-Disposition: attachment; filename=$dnfile");  
  Header("Content-Transfer-Encoding: binary");  
  Header("Pragma: no-cache");  
  Header("Expires: 0");  
 }
}
else {
 Header("Content-type: file/unknown");    
 Header("Content-Length: ".(string)(filesize("$file")));
 Header("Content-Disposition: attachment; filename=$dnfile");
 Header("Content-Description: PHP3 Generated Data");
 Header("Pragma: no-cache");
 Header("Expires: 0");
}

//다운로드실행
if (is_file($file)) {
 $fp = fopen($file, "rb");
 while(!feof($fp)) {
    echo fread($fp, 1024 * $download_size);
    sleep(1); // 무조건 속도제한 어떤 파일이나 용량이던 제한
    flush();
 }
 fclose ($fp);
}
else{
  win_close("파일이 존재하지 않습니다.");
}
?>